Image comparison tube and method of comparing radiation images

ABSTRACT

An image comparison tube stores a first image on a storage electrode and projects a deflectable second image thereon to provide an output signal dependent upon the coincidence of the two images. Electrons generated by the second image passing through the storage electrode are accelerated and focused onto a collector anode which may be a portion of an electron multiplier or a display screen.

merited tates atent [191 Nevin Feb. 5, 11974 [54] IMAGE COMPARESON TUBE AND METHQH) 3,207,997 9/1965 Eberhardt 315/11 X COMPARING RADEA'HQN [IMAGES 3,290,546 12/1966 Link et a1. 315/11 X 3,329,856 7/1967 Foote 315/11 [75] Inventor: C. Scott Nevin, Albion, 1nd. [73] Assignee: International Telephone and Primary Examiner y Wilbur Telegraph Corporation, Nutley, NJ.

[22] Filed: June 22, 1965 [21] Appl. No.: 465,922

[52] US. C1 315/11 [51] Int. Cl. H01] 31/48 [58] Field of Search 315/11, 12; 313/81 [56] References Cited UNITED STATES PATENTS 2,463,632 3/1949 Labin et a1 313/81 X 2,564,743 8/1951 Wang I 313/81 X 2,866,127 12/1958 Allwine 313/81 X Assistant Examiner-J. M. Potenza Attorney, Agent, or Firm-John T. OHalloran; Menotti J. Lombardi, Jr; Edward Goldberg [57] ABSTRAQT An image comparison tube stores a first image on a storage electrode and projects a deflectable second image thereon to provide an output signal dependent upon the coincidence of the two images. Electrons generated by the second image passing through the storage electrode are accelerated and focused onto a collector anode which may be a portion of an electron multiplier or a display screen. I

12 Claims, 7 Drawing Figures PAFENTEDFEB 51m sum 1 0F 3 PAIENEU FEB 51974 sum- 2 or 3 m? mm mw wm PNENTEDFEB 51w SHEET 3 (IF 3 IMAGE COMPARISON TUBE AND METHOD OF CQMPARING RADIATION IMAGES The present invention relates to an image comparison tube and method of comparing radiation images, and more particularly to a device and method for determining registration or correlation between a known, stored, charge image and an image of a viewed object.

The well known image dissector tube includes an extended area, planar photocathode which emits electrons in accordance with excitation of the photocathode by an optical image. The electron image so emitted by the photocathode is scanned over a small analyzing aperture so that the electrons which pass through the aperture at any instant emanate from only a single elemental area of the photocathode. The electrons which pass through the aperture are conventionally multiplied by a secondary electron multiplier to provide a timebased video output signal corresponding to the electron image which has been scanned over the aperture.

The apertureso provided is mechanical and permanent and forms the entry into an electron multiplier. In order to change the aperture in size or in shape, it

would be necessary to dismantle the tube and install a new component having the desired aperture. Quite obviously, since the tube must be evacuated, such a procedure cannot be conveniently tolerated.

If such a permanent aperture were to be given a particular size and shape, such as the letter V, it would be possible to project onto the previously described photocathode an optical image of the same shape of the letter V and then scan the electron image resulting therefrom over the analyzing aperture. Unless electrons from such electron image are passing through the aperture, obviously no signal would be generated; however, whenever an overlap occurs between the electron image and the aperture, an output signal would be generated. As the overlap progresses to the point at which the electron image coincides precisely with the aperture, a maximum signal will be generated by the multiplier inasmuch as such coincidence represents the maximum number of electrons which can pass through the aperture at any time during the scanning motion. By coupling suitable circuitry to. the tube, once the electron beam precisely coincides with the aperture, the scanning operation can be controlled and the beam thereby held in such coincidence.

It is, therefore, an object of this invention to provide an image comparison tube wherein an analyzing aperture of any desired size and shape may be electronically produced and altered at will.

It is another object ofthis invention to provide an apparatus and method for determining when an optical image ofa viewed object isregistered with a previously stored charge image.

The invention in its broader aspects includes a storage image tube having a photocathode spaced axially from a storage screen and a read-out electrode in the form of either a multiplier or phosphor screen provided on the opposite side of the storage screen for receiving electrons which pass therethrough. A focusing coil surrounds the space between the photocathode and the storage screen and serves in focusing electron images emitted by the photocathode onto the storage screen. Additionally, scanning coils or electrodes are provided between the photocathode and the storage screen for scanning or sweeping the electron image over the storage screen. Suitable potentialsare applied to the photocathode and storage screen such that a given electron image emitted by the photocathode can be stored in the form of a charge image on the storage screen. By projecting an optical image of the same size and shape as the charge image onto the photocathode, and then scanning the resulting electron image over the storage screen, the electron image will eventually come into registration with the charge image. When this occurs, the space or spaces on the storage screen occupied by the charge image will freely pass the electrons (of proper source potential) therethrough which may thereafter be focused either on a phosphor screen for providing a visual display or fed to an electron multiplier for generating an electronic signal representative of the registered condition.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a partial schematic and partial sectional view of one embodiment of this invention substantially to scale;-

FIG. 2 is a similar view of another embodiment of this invention substantially to scale;

FIG. 3 is a front view of the cathode end of the tube of FIG. 2; I

FIG. 4 is a view similar to FIGS. 1 and 2 of still another embodiment of this invention substantially to scale;

FIG. 5 is a diagrammatic illustration used in explaining the operation of this invention;

FIG. 6 is a similar diagram used in explaining the principles of this invention; and

FIG. 7 is an end view, of a typical split anode electrode which may be used in the above embodiments.

Referring now to FIG. 1, the electron discharge device of this invention, generally indicated by the numeral 10, comprises a conventional elongated evacuated envelope 11 having a longitudinal axis 12, opposite ends 13 and 14, and a cylindrical side wall 15. A conventional photoelectric cathode 16 is deposited or otherwise positioned on the inner surface of the end wall 13 which is transparent to the wavelength of the radiation to be viewed. More specifically, the photocathode 16 preferably is flat and disc-shaped, and at right angles to the axis 12 of the tube. An optical image projected onto the cathode 16 from a subject 17 causes the cathode 16 to emit low velocity electrons in a form which is an electronic duplicate of the optical image projected onto thecathode 16. Cathode 16 is coupled to a terminal 18 which is in turn adapted to be connected to a suitable source of potential.

Axially spaced from cathode 16 and in parallelism therewith is a storage electrode structure indicated generally by the reference numeral 19. Thisstructure includes a collector screen 20 and a storage screen 21 of conventional construction, these being rigidly mounted inside the envelope 11 by means of suitable supports 22. The storage screen 21 is composed of a suitable fine metallic screen or mesh of from 200 to 1,000 mesh size having an insulating material on the side facing the cathode 16. This dielectric coating has openings in registry with the wire mesh openings. The

wire mesh may be used for purposes of mechanical support, for erasure of an electrostatic charge on the dielectric, or for controlling the degree of electron penetration. The insulating or dielectric material may, for example, be magnesium flouride or zinc sulphide and additionally may be evaporated onto the wire mesh.

. For a more particular description of a storage electrode structure 19 and of the collector 20 in storage screen 21, reference may be made to the prior art which includes Farnsworth US. Pat. No. 2,754,449 issued July 10, 1956. The metallic mesh portion of the screen 21 is connected to a terminal 23 adapted to be connected to a suitable source of potential.

In order to provide for initial acceleration of the beam electrons emanating from the cathode 16 and also to provide an essentially field-free space within the envelope 11 for deflection of a beam formed from the cathode electrons, a field electrode or mesh 24 is provided extending across envelope 11 between cathode 16 and the storage electrode structure 19 and closely spaced from cathode 16, as shown. Further, this mesh electrode 24, as shown, is disc-shaped and parallel to the cathode 16. A terminal 25 is adapted to couple a suitable source of accelerating potential to the mesh 24.

A tubular electrode 26 is provided extending coaxially substantially the entire distance between the field mesh 24 and the storage electrode structure 19. This tubular electrode or cylinder 26 may be formed as a conventional conductive coating on the interior cylindrical surface of side wall 15 of the envelope 11 and may be connected to the field mesh 24 and the collector 20, or may be electrically isolated therefrom. As shown, the cylinder 26 is isolated from the mesh 24 but is connected to the collector 20. A suitable terminal 27 is connected to the cylinder 26 for supplying the latter with a suitable operating potential.

For further, detailed information regarding a suitable structure for the cathode 16, the mesh 24, and the cylinder 26, reference may be had to US. Pat. Nos. 3,329,856 issued July 4, 1967, and US. Pat. No. 3,295,010 issued Dec. 27, 1966, and assigned to the same assignee as the instant application. The pertinent disclosures of these prior patents may be regarded as being incorporated within this disclosure. Terminals25 and 27 may be connected to the same potential, or terminal 27 may be connected to a source of potential a few volts higher than that connected to terminal 25, either connection establishing an essentially field-free space within the envelope 11 between the field mesh 24 and the collector and storage screen 20 and 21, respectively, to permit magnetic deflection of an axially extending electron beam.

As viewed in FIG. 1, situated to the right of the storage screen structure 19 is a phosphor display screen or electrode 28 of conventional construction which is connected to a terminal 29 for the application thereto of a suitable accelerating potential. A suitable accelerating ring 30 of tubular shape is coaxially connected 'to the phosphor screen 28 and projects toward the storage screen 21 as shown. Another tubular accelerating ring 31 is connected to the storage screen 21 as shown and coaxially projects toward the ring 30 as shown. The two rings 30 and 31 serve in accelerating electrons from the storage screen 21 toward and against the phosphor screen 28 in the usual manner.

In order to focus the electrons emanating from the cathode 16 onto the storage screen 21 and from the latter onto the phosphor screen 28, a solenoid focusing coil 32 is provided coaxially of the tube 11 and surrounding the side wall 15. Also, suitable horizontal and vertical deflection coils 34 are mounted radially opposite the tubular electrode 27 and are disposed inside the focusing coil 32 as shown. Focusing coil 32, when suitably energized, provides a magnetic field extending axially through the envelope 11 parallel to the axis l2.

Proper focusing of an electron beam emanating from the cathode 16 onto the plane of the storage screen 21 is obtained when the cathode 16 is spaced from the storage screen 21 by an integral number of full revolutions or loops of focus, i.e., when the transit time of the electrons from the cathode 16 to the plane of the screen 21 is equal to the time required for an electron to make an integral number of complete revolutions in the magnetic field provided by the focusing coil 32. This same focusing coil 32 in cooperation with the electrodes 30, 31 and the spacing of the phosphor screen 28 from the screen 21 serves to focus electrons passed by the screen 21 onto the phosphor 28. Thus, an electron emanating from the cathode 16 may, under certain conditions, be focused directly therefrom onto the phosphor screen 28 after passing through an aperture in the screen 21. This will be explained further later on.

With suitable potentials applied to the terminals 18, 25, 27, 23 and 29, electrons from cathode 16 are given a sufficient velocity so as to produce secondary emission from the dielectric on the storage screen 21 which is greater than unity, thereby producing a positive charge image on the dielectric corresponding to the electron image emitted by the cathode 16. The development of such a charge image, the alteration thereof, the erasure and the electronic reproduction thereof are all well understood in the art of storage tubes so needs no further elaboration here.

Taking a more specifice example, and assuming that suitable potentials are applied to all of the terminals and the focusing coil 32, an optical image of an arrow 17 projected onto the photocathode 16 can and does provide a duplicate charge image on the storage screen 21. By maintaining the potentials at the proper values, this charge image on the storage screen 21 may be stored for indeterminate periods of time. Therefore, by interrupting the optical image of the subject 17 as projected onto the photocathode 16, the charge image on the screen 21 will remain.

Now, if it is assumed that the object 17 is moved slightly to one side away from its original position, and the procedure just described repeated, electrons from the cathode 16 obviously would focus onto the screen 21 at a corresponding displacement out of registry with the original, stored charge image. Under this second condition, if the potentials applied to the terminals 18, 25, 27 and 23 are altered such that the electrons approaching the storage screen 21 are of sufficiently low velocity that they will not produce secondary emission therefrom, the electrons from the second or displaced optical image position will approach a negatively charged portion of the storage screen 21 and thereby be repelled. Now, by applying suitable deflection voltages or signals to the horizontal and vertical deflection coils 33 and 34, the displaced image may be deflected inside the field-free region defined by the cylinder 26 so as to bring the second electron image into precise registry with the charge image previously stored on the screen 21. When this occurs, these second image electrons will penetrate the screen 21, because the latter is positively charged in the pattern of the stored charge image. These electrons passed by the storage screen 21 are thereupon accelerated toward and focused upon the phosphor screen 28 whereby a visual display of the object 17 will be presented. Until the electron image corresponding to the second object 17 is deflected into precise registry with the charge image on the storage screen 21, the phosphor screen 28 will remain dark. As soon as the registration occurs, the image will be displayed in its entirety in full brilliance.

However, this disparity of complete darkness and full image display on the phosphor screen 28 will not occur should some portion of the electron image as it is being scanned over the storage screen 21 coincides with a part of the charge image. Under these conditions, the electrons which are admitted by the charge image will be focused onto the display screen28, thereby displaying an image which is something less than the total of the object 17.

This may be better explained by referring to FIG. 6 wherein the object 17 has been replaced by an object of character corresponding to the letter V. This character as stored on the screen 21 is indicated by the numeral 17a.

A second V projected onto the cathode 16 which may be displaced to one side of the position of the original character projected onto the tube may assume the position indicated by the dashed line 17b. It will be noted that one leg of the dashed line V crosses one leg of the stored V such that the electrons at this crossover point can and do pass through the storage screen and onto the phosphor electrode 28. Obviously, this will produce a spot of light on the phosphor. Now, if the electron image depicted by the dashed line 17b is scanned toward the right as viewed in FIG. 6, it will eventually come into precise coincidence with the stored image 17a at which time all of the electrons composing the image 171) will pass through the storage screen and be thereupon displayed by the phosphor 28.

Any suitable scanning pattern may be employed for positioning the electron beam on the storage screen 21, and in addition to this, suitable circuitry, not disclosed herein, may be coupled to the scanning coils 33 and 34 for locking the electron beam onto the charge image once coincidence has been achieved.

Through the use of conventional electrostatic or magnetic optics (not shown), the size of the electron image focused onto the storage screen may be adjusted and made to coincide with the stored image, the relatively long distance between the cathode 16 and storage screen 21 accomodating such optics. Therefore, adjustment as to size and position of the electron image is possible.

A different embodiment of the invention is illustrated in FIGS. 2 and 3 wherein like numerals indicate like parts. This embodiment differs from that of FIG. 1 in essentially two respects, the first being the use ofa writing beam of elemental cross-section for the purpose of developing the charge image on the storage screen 21 and the second being the use of electron multipliers for obtaining a signal read-out instead of a phosphor for visual display.

In the left-hand end of the tube and interposed between the cathode 16 and field mesh 2 is mounted a control grid 35 having a terminal connection 36. This control grid 35, as shown, is in the form of a small, me-

tallic disc having a pin hole aperture 37 in the central portion thereof. As shown in both FIGS. 2 and 3, this disc 35 is mounted adjacent to the perimeter of both the cathode 16 and mesh 24 so as to be substantially out of the field of view of the cathode 16. By means of the terminal 36, any suitable, electron-modulating voltage or signal may be applied to the control grid 35 for the purpose of modulating electron flow from the cathode 16 prior to its entry into the field-free space of the cylinder 26.

By projecting a spot of light onto the cathode in the vicinity indicated by the numeral 38, electrons emitted by the cathode may, by the application of a suitable voltage onto the control grid 35, pass through the latter and onwardly in the form of a pencil-like beam toward the storage screen 21. This beam may be scanned orthogonally over the screen 21 by means of the scanning coils 33 and 34 in a raster corresponding to the commercial television, scanning raster. By imparting sufficient velocity to this electron beam, it can be caused to produce a charge image on the dielectric of the storage screen 21.

By modulating the signal applied to the control grid 35, a charge image of a particular, pre-selected pattern may be formed on the storage screen 21. Thus, through use of the control grid 35, instead of the entire cathode 16, a charge image having the same configuration as that of the arrow 17 in FIG. 1 or of the letter V in FIG. 6 may be impressed upon the storage screen 21. Use of this control grid 35 in conjunction with the electrons emitted by the photocathode 16 eliminates the need for introducing a bulky, and perhaps cumbersome, thermionic cathode which could introduce unwanted heating problems.

An electron multiplier, indicated generally by the reference numeral 39, is interposed between the storage screen 21 and a signal read-out or collector electrode indicated by the numeral 40. Any multiplier construction 39 may be used so long as it is capable of receiving and multiplying electrons passed by the storage screen 21 over the entire, cross-sectional area thereof. One such suitable multiplier, as shown in FIG. 2, utilizes a series of meshes or screens formed of secondary emissive material, these screens being disc-shaped and spaced slightly apart in parallelism so as to multiply the electron emission as it progresses from left to right through the assembly. A mesh dynode or multiplier of this type is commonly referred to as a Weiss dynode. Several of these dynodes make up the total multiplier assembly 39, each dynode, progressing in a right-ward direction, being connected to a progressively higher potential which preferably is provided by an internally mounted voltage ,divider (not shown). Such a voltage divider serves in reducing the number of terminals leading through the envelope 11. The dynodes shown in the figures are indicated by the numerals 40 through 47. Any electrons passed by the storage screen 21 are thereupon received and multiplied by the various dynodes until they are finally collected by a collector or anode 52. A suitable terminal 8 serves in coupling an anode potential to the anode 52 and also to a suitable signal-developing circuit 49. Inasmuch as magnetic focusing, as developed by the coil 32, is used, electrons emanating from a particular position on the storage screen 21 will be represented by multiplied electrons impinging on the anode 52 in about the same angular position. In other words, electron progression from the screen 21 to the anode 52 will. follow a path resembling a line parallel to the axis 12. Thus, so-called crosstalk is avoided, such cross-talk being defined as an electron path which is something other than parallel to the axis 12. The avoidance of cross-talk permits the use of an anode or collector 52 which may be split into two or more pieces indicated by the numerals 50 and 51 (FIG. 7) which are semi-circular in shape. Instead of semi-circles, quadrants or other segments of a circle may be used. By so splitting the anode into segments, and the avoidance of cross-talk in the multiplier 39, it is possible to obtain signals indicative of relative rotation between an object being viewed and the tube as well as the degree of registration between a stored image and one being viewed.

Reference is now made to FIG. 4 where again like numerals will indicate like parts. This embodiment is a composite of those of FIGS. 1 and 2 to the extent that the cathode end thereof is the same as that shown in FIG. 1 and the read-out end is the same as that shown in FIG. 2. The primary difference between the arrangement of FIG. 4 and those of FIGS. 1 and 2 is that instead of using only a single storage electrode structure 29, two such structures, substantial duplicates of each other, are used. Referring specifically to FIG. 4, it will be noted that a second tubular electrode or cylinder 26a defines a second coaxial field-free region which extends from the storage screen 21 to the second storage electrode structure 19a. Disposed immediately adjacent to the storage screen 21, and on the right-hand side thereof, is a field mesh 24a like mesh 24. This mesh 24a is of about the same size and shape as the storage screen 21 and is positioned in parallelism therewith. The cylinder 26a is connected to the storage electrode structure 19a the same as cylinder 26 to the structure 19. The collector 20a and the storage screen 21a occupy the same or similar positions as the counterpar't electrodes 20 and 21 with respect to each other and also to the cylinder 26.

As shown in FIG. 4, the two-cylinders 2 6 and 26a are of substantially the same diameter and are coaxially aligned. The structure 19 is interposed between these two cylinders 26 and 26a. The cylinder 26a preferably is twice the length of cylinder 26 to provide for easier focusing. Thus, it may be stated that there are two fieldfree regions and storage structures assembled in cascade.

In operation, an electron image produced by the cathode 16 is focused onto storage screen 21 by the same type of focusing coil shown and described in connection with FIGS. 1 and 2. The focusing coil used in this FIG. 4 embodiment preferably extends from endto-end of the tube.

After forming a charge image on the storage screen 21, this image may be transferred to the storage screen 21a by flooding the cathode 16 over its entire surface with light of uniform intensity, thereby causing the cathode to emit a floodbeam of electrons. By the application of suitable potentials to the various terminals and. electrodes, this floodbeam of electrons may be directed toward the screen 21 which passes electrons therethrough only in the regions of the charge image. These passed electrons are thereupon accelerated by the field mesh 24a and focused onto the storage screen 21a, thereby forming a charge image on the latter.

Again by the application of suitable potentials to the cathode 16 and storage screen 21, as well as the illumination of the cathode 16, the charge image on the screen 21 can be erased.

Assuming that the letter V, indicated by the numeral 17a, in FIG. 6, has been stored on the storage screen 21a, by using the procedures already explained, a second letter V 17b may be stored on the screen 21. For purposes of explanation, it may be assumed that the image on the screen 21 is not in axial registry with the image on the screen 21a.

An electron image may be formed of the charge image on the screen 21 by flooding the cathode 16 with light as previously explained, and this charge image may be focused and deflected as previously explained over the screen 21a. Once the scanned electron image is brought into registry with the charge image on the screen 21a, maximum signal output is realized from the collector 52. This maximum output signal is indicative, therefore, of registration.

By using two such storage structures 19 and 19a, it is therefore possible to store an image of an initially viewed object on the screen 21a and then subsequently store an image of either the same or a similar object on the screen 21. Since the images on the two screens 21 and 21a will remain for indeterminate periods of time, the two images may be electronically compared and studied as desired. Thus, it may be stated that the embodiment of FIG. 4 differs functionally from those of FIGS. 1 and 2 in the respect that it is capable of making comparisons of stored images whereas the arrangements of FIGS. 1 and 2 make comparisons between one stored image and a non-stored image.

While deflectionand focus described thus far has been magnetic, it should be understood that such functions may be achieved electrostatically or by a combination of electrostatic and magnetic components. However, magnetic deflection and focusing as described in combination with the storage electrode structures, pro- I vide highest resolution with minimum distortion. Use of electrostatic components permits the use of high efficiency multipliers and the splitting of electron images for producing multiple signals. A

While there have been described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.

What is claimed is:

1. A deflectable image storage tube comprising first means for producing an extended area electron beam, storage electrode means of extended area and pervious to electron flow disposed to receive said beam, means focusing said extended area beam onto said storage electrode means for developing a charge image of said beam on the latter, means providing a field-free region between said first means and said storage means through which said electron beam passes, means acting within said region upon a second beam produced by said first means for scanning said beam over said storage means, means for collecting the electrons of said second beam which pass through said storage means, and means for accelerating and focusing said electrons of said second beam onto said collecting means.

2. The tube of claim 1 wherein said collecting means includes a phosphor screen, said means for focusing and accelerating said electrons of said second beam onto said phosphor screen being positioned between said storage means and screen and including a magnetic focusing coil having an extended axial portion surrounding said tube and an electrostatic accelerating means, said means for focusing said extended area beam including another portion of said magnetic focusing coil.

3. The tube of claim 1 wherein said collecting means includes an electron collector divided into at least two electrically separated parts.

4. The tube of claim 1 wherein said collecting means includes an electron multiplier and an electroncollecting electrode for generating a signal representative of the electrons passed by said storage means.

5. The tube of claim 3 wherein said collecting means includes an electron multiplier and an electronc ollecting electrode divided into at least two electrically separated parts, and means focusing electrons from said storage means through said multiplier and onto said electron-connecting electrode, whereby at least two signals representative of the electrons passed by said storage means may be generated.

6. A deflectable image storage tube comprising an extended area photoelectric cathode which emits an electron image in response to the impingement of a radiant energy image thereon, an extended area storage electrode previous to electron flow spaced from said cathode and in a position to receive the electrons therefrom, means providing a field-free region between said cathode and said storage electrode through which electrons emitted by said cathode may flow to said storage electrode means focusing electrons emitted by said cathode onto said storage electrode for developing a charge image thereon, means acting within said region upon an electron image passing between said cathode and storage electrode for scanning said electron image over said storage electrode, means for collecting the electrons passed by said storage electrode for developing a representation thereof, and means for accelerating and focusing said electrons passed by said storage electrode onto said collecting means.

7. A deflectable image storage tube comprising an extended area photoelectric cathode which emits an electron image in response to the impingement of a radiant energy image thereon, an extended area storage electrode pervious to electron flow spaced from said cathode and in a position to receive the electrons therefrom, means providing a field-free region between said cathode and said storage electrode through which electrons emitted by said cathode may flow to said storage electrode, means focusing electrons emitted by said cathode onto said storage electrode for developing a charge image thereon, electron control means interposed between said cathode and said storage electrode for modulating a pencil-like electron beam of elemental cross-sectional area emitted by said cathode, means acting within said region upon said electron image and upon said beam for scanning the same over said storage electrode, and means for collecting electrons passed by said storage electrodes for developing a representation thereof.

8. The tube of claim 7 wherein said'cathode has a surface bounded by a perimeter, said electron control means is an electrode provided with an aperture and disposed adjacent to said cathode in overlying relation therewith next to said perimeter, the size of said control electrode being smaller than said cathode whereby said cathode may alternatively be used in part as a source of an electron-writing beam or as a source of an extended area electron image.

9. The tube of claim 7 wherein said cathode has a surface bounded by a perimeter, said electron control means is an electrode provided with an aperture and disposed adjacent to said cathode in overlying relation therewith next to said perimeter, said control electrode being further situated between said field-free region and said cathode, the size of said control electrode being smaller than said cathode whereby said cathode may alternatively be used in part as a source of an electron-writing beam or in its entirety as a source of an extended area electron image.

10. A deflectable image storage tube comprising an extended area photoelectric cathode which emits an electron image in response to the impingement of a radiant energy image thereon, an extended area storage electrode pervious to electron flow spaced from said cathode and in a position to receive the electrons therefrom, means providing a field-free region between said cathode and said storage electrode through which electrons emitted by said cathode may flow to said storage electrode, means focusing electrons emitted by said cathode onto said storage electrode for developing a charge image thereon, means acting within said region upon an electron image passing between said cathode and storage electrode for scanning said electron image over said storage electrode, a second extended area storage electrode pervious to electron flow spaced from the first-named storage electrode on the side opposite from said cathode and in a position to receive electrons from said first-named electrode, means providing a second field free region between said storage electrodes through which electrons may flow therebetween, means focusing electrons from the first-named electrode onto said second electrode for developing a charge image on the latter, means acting within said second region for scanning electrons passed by said first-named electrode over said second electrode, means for collecting the electrons passed by said second storage electrode for developing a representation thereof, and means for accelerating and focusing said electrons passed by said second storage electrode onto said collecting means.

11. The tube of claim 10 wherein said cathode and said storage electrodes are of planar construction and mounted parallel to each other, said cathode and said storage electrodes further being intersected by an imaginary straight axis centrally thereof, said axis being substantially normal to the planar extents of said cathode and said electrodes.

12. The tube of claim 10 wherein said cathode and 

1. A deflectable image storage tube comprising first means for producing an extended area electron beam, storage electrode means of extended area and pervious to electron flow disposed to receive said beam, means focusing said extended area beam onto said storage electrode means for developing a charge image of said beam on the latter, means providing a field-free region between said first means and said storage means through which said electron beam passes, means acting within said region upon a second beam produced by said first means for scanning said beam over said storage means, means for collecting the electrons of said second beam which pass through said storage means, and means for accelerating and focusing said electrons of said second beam onto said collecting means.
 2. The tube of claim 1 wherein said collecting means includes a phosphor screen, said means for focusing and accelerating said electrons of said second beam onto said phosphor screen being positioned between said storage means and screen and including a magnetic focusing coil having an extended axial portion surrounding said tube and an electrostatic accelerating means, said means for focusing said extended area beam including another portion of said magnetic focusing coil.
 3. The tube of claim 1 wherein said collecting means includes an electron collector divided into at least two electrically separated parts.
 4. The tube of claim 1 wherein said collecting means includes an electron multiplier and an electron-collecting electrode for generating a signal representative of the electrons passed by said storage means.
 5. The tube of claim 3 wherein said collecting means includes an electron multiplier and an electron-collecting electrode divided into at least two electrically separated parts, and means focusing electrons from said storage means through said multiplier and onto said electron-connecting electrode, whereby at least two signals representative of the electrons passed by said storage means may be generated.
 6. A deflectable image storage tube comprising an extended area photoelectric cathode which emits an electron image in response to the impingement of a radiant energy image thereon, an extended area storage electrode previous to electron flow spaced from said cathode and in a position to receive the electrons therefrom, means providing a field-free region between said cathode and said storage electrode through which electrons emitted by said cathode may flow to said storage electrode means focusing electrons emitted by said cathode onto said storage electrode for developing a charge image thereon, means acting within said region upon an electron image passing between said cathode and storage electrode for scanning said electron image over said storage electrode, means for collecting the electrons passed by said storage electrode for developing a representation thereof, and means for accelerating and focusing said electrons passed by said storage electrode onto said collecting means.
 7. A deflectable image storage tube comprising an extended area photoelectric cathode which emits an electron image in response to the impingement of a radiant energy image thereon, an extended area storage electrode pervious to electron flow spaced from said cathode and in a position to receive the electrons therefrom, means providing a field-free region between said cathode and said storage electrode through which electrons emitted by said cathode may flow to said storage electrode, means focusing electrons emitted by said cathode onto said storage electrode for developing a charge image thereon, electron control means interposed between said cathode and said storage electrode for modulating a pencil-like electron beam of elemental cross-sectional area emitted by said cathode, means acting within said region upon said electron image and upon said beam for scanning the same over said storage electrode, and means fOr collecting electrons passed by said storage electrodes for developing a representation thereof.
 8. The tube of claim 7 wherein said cathode has a surface bounded by a perimeter, said electron control means is an electrode provided with an aperture and disposed adjacent to said cathode in overlying relation therewith next to said perimeter, the size of said control electrode being smaller than said cathode whereby said cathode may alternatively be used in part as a source of an electron-writing beam or as a source of an extended area electron image.
 9. The tube of claim 7 wherein said cathode has a surface bounded by a perimeter, said electron control means is an electrode provided with an aperture and disposed adjacent to said cathode in overlying relation therewith next to said perimeter, said control electrode being further situated between said field-free region and said cathode, the size of said control electrode being smaller than said cathode whereby said cathode may alternatively be used in part as a source of an electron-writing beam or in its entirety as a source of an extended area electron image.
 10. A deflectable image storage tube comprising an extended area photoelectric cathode which emits an electron image in response to the impingement of a radiant energy image thereon, an extended area storage electrode pervious to electron flow spaced from said cathode and in a position to receive the electrons therefrom, means providing a field-free region between said cathode and said storage electrode through which electrons emitted by said cathode may flow to said storage electrode, means focusing electrons emitted by said cathode onto said storage electrode for developing a charge image thereon, means acting within said region upon an electron image passing between said cathode and storage electrode for scanning said electron image over said storage electrode, a second extended area storage electrode pervious to electron flow spaced from the first-named storage electrode on the side opposite from said cathode and in a position to receive electrons from said first-named electrode, means providing a second field-free region between said storage electrodes through which electrons may flow therebetween, means focusing electrons from the first-named electrode onto said second electrode for developing a charge image on the latter, means acting within said second region for scanning electrons passed by said first-named electrode over said second electrode, means for collecting the electrons passed by said second storage electrode for developing a representation thereof, and means for accelerating and focusing said electrons passed by said second storage electrode onto said collecting means.
 11. The tube of claim 10 wherein said cathode and said storage electrodes are of planar construction and mounted parallel to each other, said cathode and said storage electrodes further being intersected by an imaginary straight axis centrally thereof, said axis being substantially normal to the planar extents of said cathode and said electrodes.
 12. The tube of claim 10 wherein said cathode and said storage electrodes are of planar construction and mounted parallel to each other, said cathode and said storage electrodes further being intersected by an imaginary straight axis centrally thereof, said axis being substantially normal to the planar extents of said cathode and said electrodes, said means which provides the first-named field-free region including a first tubular electrode extending between said cathode and said first-named storage electrode, and the means providing the second region including a second tubular electrode extending between both storage electrodes, both said tubular electrodes being coaxial with respect to said axis. 